Journal ArticleCuPt ordering results in a reduction of the band-gap energy of GaInP. Thus, heterostructures and  quantum wells can be produced by simply varying the order parameter, without changing the solid  composition. Changes in the order parameter can be induced by changes in growth conditions. The  disordered/ordered/disordered quantum wells described here are grown by changing the PH3 flow  rate. Transmission electron microscopy results show that the quantum wells produced in this way  are clearly defined, with abrupt interfaces. Low-temperature photoluminescence spectra show  distinct peaks from quantum wells _x0002_QWs_x0003_ of different widths. The QW photoluminescence peak  energy increases with decreasing well width due to quantum size effects. The difference in band-gap  energy between the ordered and disordered single layers is determined from photoluminescence  excitation spectroscopy to be 0.06 eV

Hsu, Y.

Stringfellow, Gerald B.

English

The University of Utah: J. Willard Marriott Digital Library

Quantum wells due to ordering in GaInPY. Hsu and G. B. Stringfellowa)Department of Materials Science and Engineering, University of Utah, Salt Lake City, Utah 84112C. E. Inglefield, M. C. DeLong, and P. C. TaylorDepartment of Physics, University of Utah, Salt Lake City, Utah 84112J. H. Cho and T.-Y. SeongDepartment of Materials Science and Engineering, Kwangju Institute of Science and Technology,Kwangju 506-712, Korea✂Received 20 July 1998; accepted for publication 23 October 1998✄CuPt ordering results in a reduction of the band-gap energy of GaInP. Thus, heterostructures andquantum wells can be produced by simply varying the order parameter, without changing the solidcomposition. Changes in the order parameter can be induced by changes in growth conditions. Thedisordered/ordered/disordered quantum wells described here are grown by changing the PH3 flowrate. Transmission electron microscopy results show that the quantum wells produced in this wayare clearly defined, with abrupt interfaces. Low-temperature photoluminescence spectra showdistinct peaks from quantum wells ✂QWs✄ of different widths. The QW photoluminescence peakenergy increases with decreasing well width due to quantum size effects. The difference in band-gapenergy between the ordered and disordered single layers is determined from photoluminescenceexcitation spectroscopy to be 0.06 eV. © 1998 American Institute of Physics.☎S0003-6951✂98✄03352-X✆CuPt ordering is a phenomenon observed in many III/Valloys1 and has a significant effect on the band-gap energy.2For example, the band-gap energy was experimentally foundto be as much as 0.16 eV lower in partially orderedGa0.52In0.48P than in a random alloy of the samecomposition.3 A theoretical prediction of the band-gap re-duction in perfectly ordered material is 490 meV.2 The de-gree of CuPt order in GaInP is dependent on the organome-tallic vapor phase epitaxial ✂OMVPE✄ growth parameterssuch as temperature,4 input partial pressure of the P precur-sor (Pp),5 substrate orientation,6 and growth rate.7 Thus, inprinciple, it is possible to vary the degree of order, andhence, the band-gap energy, at will during growth.Heterostructures8 and quantum wells ✂QWs✄9 have been pre-pared by changing the growth temperature. However, a moreconvenient method for changing the degree of CuPt order inGaInP layers is simply to change Pp . This allows the degreeof order to be modulated simply with no other change ingrowth parameters.10 The maximum range of low-temperature band-gap energy caused by varying Pp is ap-proximately 0.07 eV.11 It is important to thoroughly charac-terize disordered/ordered/disordered ✂D/O/D✄ QW structuresin order to assess their potential for light-emitting diode andlaser applications. Preliminary studies indicate that D/O het-erostructures would be type-II,9 which will limit applicationsinvolving efficient radiative recombination.This letter presents the results of studies of disordered/ordered/disordered QWs grown by changing Pp during OM-VPE growth and of the corresponding single layers. All theGaInP layers discussed here are partially ordered. The termsordered and disordered are used throughout to refer to moreand less ordered layers, respectively. The interfaces of thequantum wells are clearly defined and abrupt in the dark-field transmission electron microscopy ✂TEM✄ images. The 5K photoluminescence ✂PL✄ peak energy from the QWs in-creases as the well width decreases, clearly demonstratingthe presence of quantum confinement.The Ga0.52In0.48P single layers and QWs were grown onsemi-insulating ✂001✄ GaAs substrates misoriented by 3° inthe (111)B direction in an atmospheric pressure, horizontalOMVPE system.12 Substrate preparation consisted of stan-dard degreasing followed by a 1 min etch in a solution of12H2O:2NH4OH:1H2O2. The substrates were then rinsed indeionized water for 5 min and blown dry with N2 beforebeing loaded into the reactor. The group III sources weretrimethylgallium at 7 °C and trimethylindium at 25 °C withPd-diffused hydrogen as the carrier gas. The phosphorussource was PH3 and the growth temperature was 670 °C witha total flow rate of 4 standard liters per minute. The group IIIflow rates were kept constant and the growth rate was 0.6✝m/h. The V/III ratios were either 30 or 480, correspondingto values of Pp of 0.75 or 12 Torr, respectively. All epilayersdiscussed here have a lattice parameter misfit ✞a/a of 0.1%, as confirmed by x-ray diffraction. Mirror-like sur-face morphologies of the epilayers were observed using Nor-marski phase contrast optical microscopy. Since there is onlyone source line for PH3 in the apparatus and it takes 60 s tochange Pp , it is necessary to switch the group III sources to‘‘vent’’ while changing Pp to avoid a transition layer.The samples were held at 5 K for PL and PL excitation✂PLE✄ spectroscopy measurements. Standard lock-in ampli-fier techniques were used. The PLE was excited with 615–680 nm light from a Coherent CR-599 dye laser with DCMdye. The ☎110✆ cross-sectional TEM samples were preparedusing standard argon-ion milling at 77 K. Dark-field imagesa✁Electronic mail: stringfellow@ee.utah.eduAPPLIED PHYSICS LETTERS VOLUME 73, NUMBER 26 28 DECEMBER 199839050003-6951/98/73(26)/3905/3/$15.00 © 1998 American Institute of PhysicsDownloaded 10 Oct 2007 to 155.97.12.90. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jspfrom superspots were obtained using a JEM 2010 scanningTEM operated at 200 kV. The undoped single layers weremeasured by the van der Pauw method and were found to ben type with a carrier concentration of ✟1016 cm✄3 and aroom-temperature Hall mobility of ✟2600 cm2/V s.Figure 1✂a  shows typical low-temperature PL and PLEspectra from an ordered Ga0.52In0.48P single layer grown un-der the same conditions (V/III☎480) as the well layers inthe D/O/D QWs. There are two PL peaks. The low-energypeak shifts to higher energy with increasing excitation inten-sity at a rate of about 5 meV/decade in agreement with ear-lier reports.13,14 The energy of the high-energy peak is nearlyindependent of excitation intensity. The PLE spectra showtwo excitonic absorption peaks due to valence-band splittingin ordered GaInP.15,16 The difference of excitonic resonancesfrom light and heavy holes is 26 meV. The band edge asdefined by the heavy-hole excitonic resonance is 1.888 eV.The data are consistent with the results of Ernst et al.15The PL and PLE spectra from a disordered single layer✁Fig. 1✂b ✆, grown under the same conditions (V/III☎30) asthe barrier layers in the D/O/D QWs, are different from thespectra in Fig. 1✂a . There is only one PL peak at an energyabout 0.02 eV lower than the absorption edge measured byPLE. The PL peak shifts to higher energy with increasingexcitation intensity at a rate of about 1 meV/decade. Thisshift rate is similar to that previously attributed toconduction-band to acceptor recombination.17 Attribution ofthe PL peak ✁Fig. 1✂b ✆ from the disordered layers toconduction-band to acceptor recombination is supported bythe growth conditions of the disordered layer. At low ✂high V/III ratios there are more group V✂III vacancies. Thegroup IV residual impurities would more likely sit on groupV ✂III  sites and become acceptors ✂donors .18 Ge and Si aretypically the residual impurities in PH3;19 C is typicallypresent due to the methyl radicals from the group III sources.Even though conduction-band to acceptor recombinationdominates in the PL spectra for the disordered layers grownat the low V/III ratio, Hall-effect measurements indicate thatthe single layer is still n type. A comparison of the PLEspectra in Fig. 1 indicates that the band-gap energy from thesingle disordered layer is 0.06 eV greater than that from thesingle ordered layer.Figure 2 shows the ✁110✆ TEM dark-field image from aD/O/D QW. The sample consists of a 270 nm barrier layergrown at Pp☎0.75 Torr, a 45 nm well layer grown at Pp☎12 Torr, another 90 nm barrier layer, a 6.5 nm well layer,and the top 90 nm barrier layer. In this dark-field image, themore ordered well layers are brighter. The interfaces be-tween the ordered and disordered layers are well defined andabrupt. The dark stripes running diagonally through the im-age are antiphase boundaries,20 i.e., interfaces between twoordered domains of the same variant with Ga and In orderingplanes out of phase.PL spectra from three D/O/D QW samples are shown inFig. 3. Each shows a band-edge peak from the barrier layersas well as distinct peaks from the two QWs. The only differ-ence in the spectra is in the peak originating from the thinnerwell, which varies in thickness from 4 to 10 nm in the threedifferent samples. It is clearly seen that the PL peak energyFIG. 1. PL ✝dashed lines✞ and PLE ✝solid lines✞ spectra for more ordered ✝a✞and less ordered ✝b✞ GaInP single layers. The arrows indicate the PLE de-tection energy.FIG. 2. Dark-field TEM image for the 6.5 nm GaInP D/O/D QW ✝thinbright region near the top✞. The 45 nm thick ordered region is also seennearer the substrate.FIG. 3. 5 K photoluminescence spectra for GaInP D/O/D QWs. The PLpeak at about 1.85 eV corresponds to the reference 45 nm well.3906 Appl. Phys. Lett., Vol. 73, No. 26, 28 December 1998 Hsu et al.Downloaded 10 Oct 2007 to 155.97.12.90. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jspfrom the QW increases with decreasing well width. Thetrend is consistent with the expected well-width dependenceof the quantized energy in QWs. These PL spectra togetherwith the TEM results definitively establish the existence ofthe quantum wells. The PL peak energies from the 10 and 45nm QWs are lower than the highest peak energy ✂ 1.88 eV✄in Fig. 1✂a✄, and hence, is lower than the band-gap energy ofthe more ordered single layer. This anomalously low energyhas previously been attributed to a type-II band alignmentbetween the two layers of the O/D heterostructure.9In summary, by simply changing the input partial pres-sure of PH3 during growth, GaInP D/O/D QWs have beensuccessfully grown. The TEM dark-field images from theorder-induced superspots show clearly defined, abrupt inter-faces between the ordered and disordered layers. The 5 K PLpeak energy from D/O/D QWs increases with decreasingwell width. This is interpreted as due to the quantum con-finement effect. The PLE spectra show that the band-gapdifference between the ordered and disordered single layersis 0.06 eV. A discussion of the peak energies and other evi-dence for a type-II band alignment between ordered and dis-ordered GaInP will be the subject of a future paper.The authors would like to thank C. Fetzer for very help-ful discussions. The work was supported by the NationalScience Foundation, the Department of Energy, and the Of-fice of Naval Research.1G. B. Stringfellow, Mater. Res. Soc. Symp. Proc. 312, 35 ✁1993☎.2K. A. Ma¨der and A. Zunger, Appl. Phys. Lett. 64, 2882✁1994☎; Phys. Rev.B 51, 10462✁1995☎.3L. C. Su, S. T. Pu, G. B. Stringfellow, J. Christen, H. Selber, and D.Bimberg, Appl. Phys. Lett. 62, 3496✁1993☎.4L. C. Su, I. H. Ho, and G. B. Stringfellow, Appl. Phys. Lett. 65, 749✁1994☎.5A. Gomyo, K. Kobayashi, S. Kawata, I. Hino, T. Suzuki, and T. Yuasa, J.Cryst. Growth 77, 367 ✁1986☎.6P. Bellon, J. P. Chevalier, E. Augarde, J. P. Andre´, and G. P. Martin, J.Appl. Phys. 66, 2388✁1989☎; L. C. Su, I. H. Ho, and G. B. Stringfellow,ibid. 75, 5135 ✁1994☎.7D. S. Cao, E. H. Reihlen, G. S. Chen, A. W. Kimball, and G. B. String-fellow, J. Cryst. Growth 109, 279✁1991☎.8L. C. Su, I. H. Ho, N. Kobayashi, and G. B. Stringfellow, J. Cryst. Growth145, 140✁1994☎.9R. P. Schneider, Jr., E. D. Jones, and D. M. Follstaedt, Appl. Phys. Lett.65, 587 ✁1994☎.10Y. S. Chun, Y. Hsu, I. H. Ho, T. C. Hsu, H. Murata, G. B. Stringfellow, J.H. Kim, and T.-Y. Seong, J. Electron. Mater. 26, 1250 ✁1997☎.11H. Murata, T. C. Hsu, I. H. Ho, L. C. Su, Y. Hosokawa, and G. B.Stringfellow, Appl. Phys. Lett. 68, 1796✁1996☎.12T. Y. Wang, K. L. Fry, A. Persson, E. H. Reihlen, and G. B. Stringfellow,J. Appl. Phys. 63, 2674✁1988☎.13M. C. DeLong, W. D. Ohlsen, I. Viohl, P. C. Taylor, and J. M. Olson, J.Appl. Phys. 70, 2780 ✁1991☎.14P. Ernst, C. Geng, G. Hahn, F. Scholz, H, Schweizer, F. Phillipp, and A.Mascarenhas, J. Appl. Phys. 79, 2633✁1996☎.15P. Ernst, C. Geng, F. Scholz, H, Schweizer, Y. Zhang, and A. Mascaren-has, Appl. Phys. Lett. 67, 2347✁1995☎.16S. H. Wei, A. Franceschetti, and A. Zunger, Mater. Res. Soc. Symp. Proc.147, 3 ✁1996☎.17 J. Chevallier and A. Laugier, Phys. Status Solidi A 8, 437✁1971☎; R. C. C.Leite, Phys. Rev. 157, 672 ✁1967☎.18T. Nakanisi, J. Cryst. Growth 68, 282 ✁1984☎.19G. B. Stringfellow, Organometallic Vapor Phase Epitaxy: Theory andPractice, 2nd ed. ✁Academic, San Diego, CA, 1998☎, Chap. 3.20L. C. Su, I. H. Ho, and G. B. Stringfellow, J. Appl. Phys. 75, 5135✁1994☎.3907Appl. Phys. Lett., Vol. 73, No. 26, 28 December 1998 Hsu et al.Downloaded 10 Oct 2007 to 155.97.12.90. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsp

Quantum wells due to ordering in GaInP

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Quantum wells due to ordering in GaInP

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